Train storage and humidity.

If it's silica gel, it's safe. If it's not, get some silica gel. Desiccant. Don't let it come in contact with the trains.

By the way, when are we going to connect the Yukon Route with the Alaska RR?

Hers's what I use in each and every storage box. Large enough that you don't have to worry about it and rechargeable if needed.

  Hydrosorbent Silica Gel Desiccant Dehumidifier 200 Gram (Protects 15 Cubic Feet) Box

I have occasionally found it cheaper on that well known auction site.  

Remember what Chris said, desiccant has to be baked out, or "recharged" to be useful once it's exposed to ambient for any length of time.  If the box is not sealed, it's exposed to ambient air.

The tiny packets that are in model train shipping boxes are 99% placebo, and 1% protection, not nearly enough to offer real protection.  Once you've opened the box and exposed it to ambient air, it's 100% placebo until you at least bake the moisture out of it again.

In Chris's link, note this: 4"L x 2"'W x ½"T, protects 3 Cubic Feet

Think about how many of those little packets would fit in that space and consider how much (or how little) protection they're really offering.  If you're going to desiccant to actually protect something, use a sufficient amount.